I know this topic has come up before; I've walked through a dozen threads on it, but I'm still not convinced that the "acceptable margin for error on your printer" is the answer. Quick walk-through:

Printing playing cards, two rows of four on 8.5x11 paper. I have one document for the fronts, one for the back.

I'm not having the printer print double sided -- I print one side, feed the paper back through to print the other side.

I printed hundreds of sheets like this over the past three months while prototyping a game. The front and back aligned every time with such a small margin for error that it was unnoticeable when the cards were cut out.

Installed InDesign on a new laptop and can't get a single front and back aligned now. This includes files that I produced on the old machine which previously lined up perfectly.

It's incredibly consistent -- there's an additional .0625 inch to the right margin on the landscaped pages. And it's .0625 every time. Someone made the comment that if you print front/back 10 times you'll get 8 variations. Point taken, but not happening here. The change is extremely consistent.

It seems like I must have a setting in InDesign adding that extra bit of margin to both new and old documents at print time, but I can't find it anywhere. Copying my print profile summary below and would certainly appreciate any guesses or insights that people have to offer.

Nope, I double checked that -- everything's lined up the same in the InDesign doc. It's easy to check, since they're standard playing card size at 2.5" x 3.5". Also, I have fourteen different files that lay out different decks/backs via data merge. Wouldn't totally discount the idea that I could somehow bump each of them, but it's more likely a setting that I tweaked (or didn't tweak) globally.

Ah, that could be it. It's a brand new laptop and it auto-detected the printer on the network, so it's possible that I had a specific driver installed on my old laptop and a generic one on this machine. I'll give that a try this morning. Thanks!

So, some interesting results after experimentation. Although I was never able to get PPD to show up in the selection in Adobe, I did finally get the print to align again.

First, I re-installed InDesign on my old laptop and moved the files over there. Printed -- and everything lined up perfectly. The only difference in setup is that the old laptop had a much older driver for my HP printer. I wasn't able to find the driver file to install on the new laptop, though; I could only get a more current driver, and never fixed that shift.

Next thing, I found that when I exported the pages to PDF and printed on either machine, the two sides lined up perfectly again. I don't know what the explanation is here. Print the document directly from InDesign and got that shifting effect. Printed from PDF, worked fine.

Finally, I got a new Brother printer. (I was looking for one that had a lot better ink efficiency since I'm printing a lot of card prototypes.) Installed the base driver on the new laptop, the two sides are aligning great whether I print from InDesign or PDF.

TLDR; my problem appears to have been solved, though I can't say that I actually solved it.